Various techniques are known in the prior art for the reformation of hydrocarbons and particularly for the reformation of lower hydrocarbons, such as natural gas, in order to produce hydrogen. Most of these techniques involve the production of steam in a natural gas fired furnace which also preheats the hydrocarbon stream to be reformed. The combined steam and hydrocarbon stream are then catalytically reformed in a reaction zone which is heated by the combustion products of the fired natural gas. In order to be thermodynamically efficient, such fired catalytic reformers require excess heat which can then be utilized to produce steam for use in the process or for export to outside consumption. Such a design creates an efficiency problem when sufficient steam requirements are not present near the reformation operation. In that event, expensive excess steam is produced which cannot be economically utilized.
In addition, it is known in the prior art to utilize multiple stages of reformation to produce hydrogen, such as is taught in U.S. Pat. No. 3,264,066. In that patent the staged serial reaction of hydrocarbons with steam to produce hydrogen is effected in a step wise manner wherein initial reaction occurs in the primary reformer and further complete reaction occurs in the secondary reformer wherein the reformation occurs on the same feed stream.
It is also known to heat exchange a reforming stream against a reformed stream in a fired catalytic reformer in order to effect energy efficiencies in the reformation reaction. This is disclosed in U.S. Pat. No. 4,071,330 wherein a feed stream is introduced into a longitudinal reactor and then returns as a product stream longitudinally back through the reactor in indirect heat exchange with the feed coming into the reactor. Additional heat is supplied by a fired burner which is segregated from the reaction streams.
It is further known to perform steam reformation to produce hydrogen in a reactor wherein tubular conduits situated in an array are provided with catalyst packing therein in order to perform the reformation reactor. In U.S. Pat. No. 4,113,441 such a system is disclosed wherein all of the heat of reaction is produced by an external stream which heat exchanges indirectly with the catalyst tubes. The reformation product is centrally removed in an axially aligned exit tube.
Finally, it is known to reform hydrocarbons in an indirect heat exchange with previously reformed product from a primary and secondary reformer wherein the product of the indirect heat exchange reformation is kept discrete from the reformed product which provides heat for the indirect heat exchange reformation. This is disclosed in U.S. Pat. No. 4,162,290 wherein a primary, secondary and tertiary reformer are utilized in which the tertiary reformer is an exchanger-reactor.
Additional art of interest includes U.S. Pat. No. 4,079,017, U.S. Pat. No. 4,098,587, U.S. Pat. No. 4,098,588 and U.S. Pat. No. 4,098,589.